Welded airbag cushion comprising sewn reinforcement seams

ABSTRACT

An airbag construction utilizing welds, reinforced with sewn seams, to adhere two fabrics together to form an inflatable airbag cushion. Although welded seams provide better and more easily produced attachment points between multiple layers of fabrics, not to mention improved manners of reducing air or gas permeability at such attachment points, the utilization of sewn seams adjacent to such welded areas provides stronger reinforcement, and thus more reliable nonpermeable fabrics. Seam welding generally concerns the utilization of a film on the underside of a fabric which, upon contact with a second, film-treated fabric and upon exposure to high frequency energy, forms a bead of polymeric material at the attachment point between the two fabric layers. Lower numbers of sewn seams may be utilized to permit sufficient reinforcement if the size of the formed polymeric bead is of sufficient size to permit thorough sealing and adhesion between the fabric layers. Such a specific reinforced fabric, as well as high bead-size welded airbag fabrics are encompassed within this invention.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 09/406,000,filed on Sep. 24, 1999 now U.S. Pat. No. 6,364,356 B1. This parentapplication is herein entirely incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a method utilizing welds, reinforcedwith sewn seams, to adhere two fabrics together to form an inflatableairbag cushion. Although welded seams provide better and more easilyproduced attachment points between multiple layers of fabrics, not tomention improved manners of reducing air or gas permeability at suchattachment points, the utilization of sewn seams adjacent to such weldedareas provides stronger reinforcement, and thus more reliablenonpermeable fabrics. Seam welding generally concerns the utilization ofa film on the underside of a fabric which, upon contact with a second,film-treated fabric and upon exposure to high frequency energy, forms abead of polymeric material at the attachment point between the twofabric layers. Lower numbers of sewn seams may be utilized to permitsufficient reinforcement if the size of the formed polymeric bead is ofsufficient size to permit thorough sealing and adhesion between thefabric layers. Such a specific reinforced fabric, as well as highbead-size welded airbag fabrics are encompassed within this invention.

BACKGROUND OF THE PRIOR ART

All U.S. patents cited herein are hereby fully incorporated byreference.

Inflatable protective cushions used in passenger vehicles are acomponent of relatively complex passive restraint systems. The mainelements of these systems are: an impact sensing system, an ignitionsystem, a propellant material, an attachment device, a system enclosure,and an inflatable protective cushion. Upon sensing an impact, thepropellant is ignited causing an explosive release of gases filling thecushion to a deployed state which can absorb the impact of the forwardmovement of a body and dissipate its energy by means of rapid venting ofthe gas. The entire sequence of events occurs within about 30milliseconds. In the undeployed state, the cushion is stored in or nearthe steering column, the dashboard, in a door, or in the back of a frontseat placing the cushion in close proximity to the person or object itis to protect.

Inflatable cushion systems commonly referred to as air bag systems havebeen used in the past to protect both the operator of the vehicle andpassengers. Systems for the protection of the vehicle operator havetypically been mounted in the steering column of the vehicle and haveutilized cushion constructions directly deployable towards the driver.These driver-side cushions are typically of a relatively simpleconfiguration in that they function over a fairly small well-definedarea between the driver and the steering column. One such configurationis disclosed in U.S. Pat. No. 5,533,755 to Nelsen et al., the teachingsof which are incorporated herein by reference.

Inflatable cushions for use in the protection of passengers againstfrontal or side impacts must generally have a more complex configurationsince the position of a vehicle passenger may not be well defined andgreater distance may exist between the passenger and the surface of thevehicle against which that passenger might be thrown in the event of acollision. Prior cushions for use in such environments are disclosed inU.S. Pat. No. 5,520,416 to Bishop; U.S. Pat. No. 5,454,594 to Krickl;U.S. Pat. No. 5,423,273 to Hawthorn et al.; U.S. Pat. No. 5,316,337 toYamaji et al.; U.S. Pat. No. 5,310,216 to Wehner et al.; U.S. Pat. No.5,090,729 to Watanabe; U.S. Pat. No. 5,087,071 to Wallner et al.; U.S.Pat. No. 4,944,529 to Backhaus; and U.S. Pat. No. 3,792,873 to Buchneret al.

The majority of commercially used restraint cushions are formed of wovenfabric materials utilizing multifilament synthetic yams of materialssuch as polyester, nylon 6 or nylon 6,6 polymers. Representative fabricsfor such use are disclosed in U.S. Pat. No. 4,921,735 to Bloch; U.S.Pat. No. 5,093,163 to Krummheuer et al.; U.S. Pat. No. 5,110,666 toMenzel et al.; U.S. Pat. No. 5,236,775 to Swoboda et al.; U.S. Pat. No.5,277,230 to Sollars, Jr.; U.S. Pat. No. 5,356,680 to Krummheuer et al.;U.S. Pat. No. 5,477,890 to Krummheuer et al.; U.S. Pat. No. 5,508,073 toKrummheuer et al.; U.S. Pat. No. 5,503,197 to Bower; and U.S. Pat. No.5,704,402 to Bowen et al.

As will be appreciated, the permeability of an airbag cushion structureis an important factor in determining the rate of inflation andsubsequent rapid deflation following the impact event. Different airbagcushions are utilized for different purposes. For instance, some airbagcushions are installed within inflation modules for driver protectionwithin the steering column of an automobile. Others are utilized asprotection for front seat passengers and are installed in and around theglove compartment and/or on the dashboard in front of such a passengerseat. Still others have been developed in an effort to protect allpassengers during a long-duration impact event, such as, for example, arollover collision. In those types of crashes, the target airbag cushionmust inflate quickly under high pressure (such as between about 40 and50 psi) and remain inflated at relatively high pressures in order toprovide the greatest degree of protection to such passengers.Furthermore, such long-duration airbag cushions preferably comprise“pillow” formations created through the attachment of at least twodifferent fabrics or fabric ends together and sealed, sewn, or the like,together. Upon inflation the free space between the attachment pointsinflate as well, thereby producing the desired cushioned “pillow”structures. Such long-duration, “pillowed” structures have beendisclosed in the prior art as airbag cushions within U.S. Pat. No.5,788,270 to Haland. However, in order to provide a suitable, effectiveairbag fabric and cushion comprising two or more points of attachmentbetween fabrics or fabric ends, there has been a need to improve uponthe structural integrity of the seams at such attachment points toprevent unwanted and potentially harmful leakage of gas or air fromwithin the target airbag cushion. The prior art has discussed thedevelopment of coatings to place over the sewn seams at such attachmentpoints in order to seal the potentially loose portions of such seamsand/or to keep the individual yams of the airbag fabrics at theattachment points stationary in order to prevent yam shifting and thuspossible openings for air or gas leakage. However, such coatings havenot proven fully capable of providing such needed benefits. Mostcoatings comprise silicones which actually tend to act as yam lubricantsand thus not only do not prevent, but permit deleterious yarn shifting.Also, the amount and/or thickness required of such coatings isrelatively high which creates a tackiness problem between fabricsportions during storage in an inflation module. When the airbag cushionis packed tightly in such closed quarters, the coatings may tend toincrease the adhesiveness between the contacting fabric portions whichmay consequently create difficulties in unfolding of the cushion uponinflation. Furthermore, such thick coatings are rather costly and thusincrease the overall price passed on to the consumer. In recent years,there has been a tremendous push to producing highly effective airbagcushions while simultaneously lowering the costs associated with suchproduction. Thus, some manner of providing proper, well-performing,cost-effective attachment points between airbag fabrics or airbag fabricends is necessary to meet these industry requirements. To date, theprior art has not accorded such an improvement in performance and costto the airbag cushion market.

SUMMARY OF THE INVENTION

In view of the foregoing, it is a general object of the presentinvention to provide an effective, reinforced, welded airbag fabric forincorporation within an airbag cushion for utilization within a vehiclerestraint system. The term “vehicle restraint system” is intended tomean both inflatable occupant restraining cushion and the mechanical andchemical components (such as the inflation means, ignition means,propellant, and the like). It is a more particular object of the presentinvention to provide an airbag fabric wherein the reinforcement seam issewn in an area adjacent to the welded seam. A further object of thisinvention is to provide an airbag fabric which comprises attachmentpoints connected and held in place through the utilization of relativelylarge polymeric beads.

To achieve these and other objects and in accordance with the purpose ofthe invention, as embodied and broadly described herein, the presentinvention provides an airbag fabric for incorporation within an airbagcushion comprising at least one welded seam as a point of attachmentbetween two fabric panels, wherein said airbag fabric also comprises atleast one sewn seam located adjacent to said welded seam. This inventionalso encompasses an airbag fabric for incorporation within an airbagcushion comprising at least one welded seam as a point of attachmentbetween two fabric ends, wherein said welded seam comprises a polymericbead having an average thickness of from about 2 to about 40 mils.

The term “welded seam” encompasses any attachment point between twopanels of fabric through the utilization of a welding process. Ingeneral, such a process entails the film-coating of the fabric panelswith a polymeric dipolar thermoplastic material; contacting thefilm-coated panels; placing a high intensity electron discharging moldover the designated area of the fabric in which a seam is to beproduced; applying such a high intensity electron field to thefilm-coated fabric panels which consequently makes the electrons withinthe dipolar thermoplastic material to move from one pole to the otherthereby creating friction which ultimately produces heat; and throughthe exposure to such heat, forming elongated polymeric beads whichadhere to both fabric panels and fill the interstitial space between thefabric panels (the term “fabric panels” connotes either the utilizationof two different, separate pieces of fabric or two different ends of onefabric which are joined together through such a welding process). Suchpolymeric beads bear the load upon the attachment points created by thehigh pressure of inflation. However, the contact zone between the beadsand the fabric panels will substantially encompass merely the topportion of such beads. Consequently, there still exists a possibilitythat the polymeric beads will not be able to prevent tearing of thepanels from the beads due to such a low contact surface area.

Thus, although seam welding, which is more fully discussed in U.S.patent application Ser. No. 09/326,368 now U.S. Pat. No. 6,344,251 B1 toKeshavaraj et al., produces excellent and strong seam attachments inorder to substantially prevent tearing of the airbag fabric panelsduring inflation, the airtight structure produced by such polymericbeads may be compromised through the incomplete securing of the bead tothe fabric. The inventive fabric thus improves upon this potentiallyproblematic effect by securing more of the fabric around the beads afterthey have been elongated and cooled (welded) into the fabric structure.The sewn seam must be present in an area adjacent to the welded seam. Byadjacent, it is meant that the sewn seam is produced either between twodifferent attachment points (thus producing a seam between the weldedseams) or, if only one welded seam is present, at a distance closer tothe edges of the fabric panels than the welded seam but close enough toincrease the amount of fabric in contact with the polymeric bead of thewelded seam. Generally, such a distance is from about 0.1 cm to about 5cm; preferably from about 0.1 cm to about 3 cm; more preferably fromabout 0.5 cm to about 2 cm; and most preferably from about 0.5 to about1 cm. The length of the sewn seams is not important, although asufficient length is necessary to ensure sufficient contact between thepolymeric beads and the fabric. Too short a length will not create asufficient contact surface area; too long may interfere with theperformance of the remaining portions of the airbag fabric. The term“sewn seam” is intended to encompass any type of seam produced byrepeated stitching such as through the use of needle stitches,ultrasonic stitches, and the like. Any type of strong, industrial threadmay be utilized which provides the necessary reinforcement strength tothe welded seam. Thus, any size thread from about #40 to about #200 maybe utilized. The seam may be single-needle, preferably; however,multiple needle stitching may also be performed.

Another method of increasing the strength of the welded seam is toincrease the overall thickness of the polymeric bead produced by such aprocess. This thickness increase will increase the contact surface areabetween the bead and the fabric thereby filling more interstitial spaceas well and ultimately reducing the potential for air or gas leaksthrough the airbag fabric. It has been found that this alteration ofstandard RF-welding techniques is the only manner to facilitateproduction of more leak-resistant fabrics. Theoretically, a modificationof the geometry of such polymeric beads would also result in bettercontact between with the target fabric; however, such geometricalalterations is very difficult to accomplish since the polymeric film,during the welding process, orients itself to a spherical shape moreeasily and readily than other configurations. Thus, a bead thickness ofat least four times the thickness of the polymeric film coating on thetarget fabric is necessary to effectuate the desired elongation andresultant adhesion of the bead to the fabric. Since such polymeric filmcoatings exhibit average thicknesses of from about 0.5 to about 10 mils,the preferred bead average thickness should be from about 2 to about 40mils; preferably from about 5 to about 40 mils; more preferably fromabout 10 to about 30 mils; and most preferably from about 20 to about 30mils. To produce such a thick bead, a weld head must be utilized whichrequires a thickness itself of greater than 2,000 times the thickness ofthe film on the fabric surface. Thinner bead structures produceinconsistent weld strengths within the target fabrics since thedirection of molten polymer flow over the fabric surface is verydifficult to control, particularly if the curved area or straight-linearea at the point of attachment of the fabric panels is not uniform. Thethicker bead production substantially reduces these problems ofnon-uniformity in the fabric structure by providing more polymer surfacearea for a greater amount of fabric-bead contact. The bead will deformduring welding to fill the open spaces between the fabric panels andcover a wider area of the fabric panels, particularly around theattachment points. Such an increase in surface coverage and spacefilling thus permits the production of a more robust seam than underpreviously known seam-welding techniques.

Even with the utilization of such an improved seam production method,there still remains a possibility for unraveling, tearing, or seamfailure within the fabric due to insufficient bead-fabric contact. Asnoted above, this potential problem may be corrected through theutilization of a sewn seam adjacent to the welded seam.

PREFERRED EMBODIMENT OF THE INVENTION

The Examples below are indicative of the particularly preferredembodiment within the scope of the present invention:

EXAMPLE 1

Two woven fabrics, each comprising 420 denier nylon-6,6 yarns andexhibiting a 39×39 picks/ends per inch construction, were coated with2.4 ounces of a standard polyurethane airbag coating plus an adhesionpromoter applied to one side of each target fabric. The coated surfaceswere then contacted together and a weld head was placed over thetwo-fabric composite. The two-fabric composite was then exposed to ahigh frequency electromagnetic field reversing itself in excess of 27million times per second (27 MHz) which eventually heated up the film atthe proposed weld location between the two fabrics. The resultant beadsproduced through such a procedure created a welded seam of approximately3 mm over the entire length of the two fabrics, thereby connecting thefabrics at one location. After cooling, the fabrics were thentransported to a sewing machine. A seam was then sewn with a #138 threadthrough a single #140 needle, exhibiting about 20 stitches per 100 mm ofseam length parallel to the welded seam and about 5 mm from the weldedseam. The tear strength of the two seams was beyond that required forstandard airbag products (i.e., greater than about 275 pounds per foot).

EXAMPLE 2

Two woven fabrics, each comprising 210 denier nylon-6,6 yarns andexhibiting a 55×55 picks/ends per inch construction, were coated with2.7 ounces of a standard polyurethane airbag coating plus an adhesionpromoter applied to one side of each target fabric. The coated surfaceswere then contacted together and a weld head was placed over thetwo-fabric composite. The two-fabric composite was then exposed to ahigh frequency electromagnetic field reversing itself in excess of 27million times per second (27 MHz) which eventually heated up the film attwo adjacent proposed weld locations between the two fabrics. Electrodeseach having widths of approximately 6 mm, aproximately 3 mm apart, overthe entire length of the two fabrics were utilized, thereby connectingthe fabrics at one location. After cooling, the fabrics were thentransported to a sewing mahcine. A seam was then sewn with a #92 threadthrough a single #140 needle, exhibiting about 40 stitches per 100 mm ofseam length parallel to the welded seam and about 5 mm from the weldedseam. The tear strength of the two seams was beyond that required forstandard airbag products (i.e., greater than about 275 pounds per foot).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides an aerial view of a portion of an inventive airbag witha magnified view of the inventive sewn (stitched) seam located betweentwo welded seams.

FIG. 2 depicts a cross-sectional view of the magnified portion of FIG.1.

DETAILED DESCRIPTION OF THE DRAWINGS

As depicted in FIG. 1, a side curtain airbag 10 with individual pillowedcompartments 12, 14, 16, 18, 20, 22, as examples (uninflated asdepicted), formed through the utilization of welded seams 24 (as anexample). As shown in the magnified view of the welded seams 24, thereare two welded seams 26, 28, with a single stitched (sewn) seam 30located adjacent to both to provide increased tear strength as notedabove in the EXAMPLEs.

In FIG. 2, the welded seams 24 are more easily seen in cross-section asthe two welded polymeric beads 26, 28 having average thicknesses ofbetween 20 and 30 mils are separated by an adjacently located stitchedseam 30. Again, such a configuration provides increased tear strength asnoted above.

While specific embodiments of the invention have been illustrated anddescribed, it is to be understood that the invention is not limitedthereto, since modifications may certainly be made and other embodimentsof the principals of this invention will no doubt occur to those skilledin the art. Therefore, it is contemplated by the appended claims tocover any such modifications and other embodiments as incorporate thefeatures of this invention which in the true spirit and scope of theclaims hereto.

What I claim is:
 1. An airbag fabric cushion comprising at least twofabric layers, wherein at least one welded seam is present as a point ofattachment between said at least two fabric layers, wherein said atleast two fabric layers each exhibit an internal portion in relation tosaid airbag cushion and an external portion in relation to said airbagcushion, wherein said airbag cushion also comprises at least onestitched reinforcement seam located either between two differentattachment points or, if only one welded seam is present, at a distancecloser to the edges of said at least two fabric layers than said weldedseam, wherein the stitches within said at least one stitchedreinforcement seam pass through both the internal and external portionsof said at least two fabric layers; wherein said at least one stitchedreinforcement seam exhibits a tear strength in excess of that associatedwith standard airbag inflation pressures.
 2. The airbag cushion of claim1 wherein said stitched reinforcement seam is formed by thread-stitchingor ultrasonic-stitching.
 3. An airbag fabric cushion comprising at leasttwo fabric layers, wherein at least one adhesive seam is present as apoint of attachment between said at least two fabric layers, whereinsaid at least two fabric layers each exhibit an internal portion inrelation to said airbag cushion and an external portion in relation tosaid airbag cushion, wherein said airbag cushion also comprises at leastone stitched reinforcement seam located either between two differentadhesive seams or, if only one adhesive seam is present, at a distancecloser to the edges of said at least two fabric layers than said weldedseam, wherein the stitches within said at least one stitchedreinforcement seam pass through both the internal and external portionsof said at least two fabric layers; wherein said at least one stitchedreinforcement seam exhibits a tear strength in excess of that associatedwith standard airbag inflation pressures.
 4. The airbag cushion of claim3 wherein said stitched reinforcement seam is formed by thread-stitchingor ultrasonic-stitching.